1. Field of the Invention
The present invention relates to a wire bonding apparatus, and more particularly, to a wire bonding apparatus that is equipped with a movable torch electrode.
2. Prior Art
In a movable torch electrode system, the torch electrode is installed so that it can move horizontally. The torch electrode is positioned beneath the tip end of the wire extending from the tip end of the capillary and is caused to discharge so as to form a ball on the tip end of the wire. Following this ball formation, the torch electrode is retracted from beneath the capillary.
Japanese Patent Application Publication (Kokoku) No. H1-58861 and Japanese Patent Application Laid-Open (Kokai) No. H9-205110 disclose bonding apparatuses equipped with movable torch electrodes of the type described above.
In Japanese Patent Application Publication (Kokoku) No. H1-58861, a metal electrode is formed at the tip end of the capillary, so that an electrical arc can be produced between the metal electrode and the movable torch electrode.
The movable torch electrode system of Japanese Patent Application Laid-Open (Kokai) No. H9-205110 includes an actuator that comprises a lateral actuating arm, a spring, a stopper and a solenoid. The actuating arm is installed so as to be movable in a horizontal direction, and a torch electrode is attached to this actuating arm. The spring pulls the lateral actuating arm toward the area beneath the capillary. The stopper positions the lateral actuating arm beneath the capillary, and the solenoid drives the lateral actuating arm so that the torch electrode is retracted from beneath the capillary.
When the solenoid is switched on, the lateral actuating arm is pulled by the magnetic force of the solenoid so that the torch electrode is retracted from beneath the capillary. When the solenoid is switched off, the lateral actuating and is caused to move beneath the capillary by the driving force of the spring, and it stops when the torch electrode contacts the stopper.
In the prior art described above, the torch electrode is stopped by way of causing the electrode to come into contact with a stopper. However, this leads to noise and causes dust as a result of wear. Furthermore, since the range of movement of the torch electrode is limited by the solenoid and stopper, there is no degree of freedom in the position of the torch electrode, and the torch electrode constitutes an obstacle. Thus, the working characteristics of wire threading, capillary replacement, etc. tend to be poor. Moreover, since driving is accomplished by a spring and solenoid, the speed of the apparatus cannot be increased.
Accordingly, the inventors of the present application invented a wire bonding apparatus in which the torch electrode is directly coupled to the output shaft of a pulse motor (Japanese Patent Application No. H11-35283). This wire bonding apparatus is superior in terms of quiet operation and in terms of working characteristics since the movement range of the torch electrode has a high degree of freedom. Also, it can increase the speed of the apparatus. However, in conventional pulse motor control methods, vibration of the torch electrode occurs with each pulse, and the residual vibration at the time of stopping is especially violent.
Accordingly, the object of the present invention is to provide a wire bonding apparatus that can minimize vibration of torch electrode and that is quiet in operation, has excellent working characteristics with high movement range of the torch electrode, and can increase the speed of the bonding apparatus.
The above object is accomplished by a unique structure of the present invention for a wire bonding apparatus which is equipped with a capillary through which a wire is passed, a torch electrode which is installed in a substantially horizontally movable manner so that the torch electrode is positioned beneath the capillary, and a torch electrode driving means which drives the torch electrode; and in the present invention, the torch electrode is directly coupled to the output shaft of a pulse motor, and this pulse motor is driven by a high-resolution angle control circuit.
In the above structure of the present invention, the resolution of the pulse motor obtained by the high-resolution angle control circuit is 30,000 parts per revolution or greater.